Synthesis and mechanistic studies of cobalt catalysts in the formation of pyridines; mechanistic investigation of ruthenium catalyzed yne-ene metathesis for 1,3-butadienes

The cobalt(I)-catalyzed cyclotrimerization of two alkynes and one nitrile in aqueous solution is reported in Chapter 1. This transformation is catalyzed by a new water-soluble Co(I) catalyst that operates at a low catalyst loading in aqueous conditions. Only stoichiometric amounts of reagents are necessary for the transformation and the robust nature of the system precludes the need for protecting group chemistry. Kinetic data suggest a first order dependence on nitrile concentration for product formation and double isotopic crossover experiments suggest an associative mechanism.; Chapter two describes experiments that helped elucidate the mechanism of the first steps in the cyclotrimerization transformation. Isotopic crossover data suggest the formation of a coordinatively unsaturated intermediate much faster than formation of a metallacycle intermediate, invoking a dissociative mechanism for metallacycle formation. The first crystal structure of a catalytically active cobaltacycle intermediate containing a carbonyl and hydroxyl on the Cp ring are also reported.; Chapter three describes the synthesis and testing of new Co(I) cyclotrimerization catalysts that have electron withdrawing groups attached to the Cp ring. Through the use of palladium-catalyzed cycloadditions, followed by bromination and elimination of the resulting cyclopentane rings, new Cp rings were prepared. The Cp rings were then used in the successful synthesis of new Co(I) cyclotrimerization catalysts which were shown to be more active catalysts than those commonly used for the cyclotrimerization reaction. The first example of a sulfone substituted Cp ring is also reported.; Chapter four details a mechanistic study for the intermolecular enyne metathesis reaction for the synthesis of dienes catalyzed by Grubbs' ruthenium(IV) catalyst. High concentrations of ethylene and low concentrations of alkyne appear to lead to higher yields of diene and increased rates of reaction. There is an inverse linear phosphine dependence, and kinetic isotope effects suggest rate-determining breakdown of a metallacyclobutene intermediate.